Spot if brownish blood then nothing...

I was supposed to start my period today. I got a spot of brownish blood and I thought.... well I am out.... put on a pad to see when I would actually start prior to going to tampons (usually just an hour or so).... the end of the day and nothing. One more brown spot when I wiped after peeing, but nothing else..... it's just weird. I have taken pregnancy tests and all were a BFN, not sure what the delay is..... It is just frustrating. Do I put this in my calendar as I started? Do I mark it as I missed? Why the heck would it be late? It's too late for implantation bleeding. Any insight as to what is going on?

Update #2:

I am on day two of nothing all day except one brownish spot (pic below.... sorry tmi)...

I made an appointment with my OBGYN for Thursday. If I haven't started by then I will have her run labs.... just not sure what is going on....

Update #3:

AF finally showed.... so I am out.